from math import *
PI = 3.1415926535898
while True:
    try:
    	k = raw_input()
    	if len(k) > 0:
	    	a, b, x, y = map(float, k.strip().split(' '))
	    	print pow((a-x)*(a-x)+(b-y)*(b-y), 0.5)
    except EOFError:
        break from math import * PI = 3.1415926535898 PI 3.1415926535898 while True:
    try:
    	k = raw_input()
    	if len(k) > 0:
	    	a, b, x, y = map(float, k.strip().split(' '))
	    	print pow((a-x)*(a-x)+(b-y)*(b-y), 0.5)
    except EOFError:
        break True try:
    	k = raw_input()
    	if len(k) > 0:
	    	a, b, x, y = map(float, k.strip().split(' '))
	    	print pow((a-x)*(a-x)+(b-y)*(b-y), 0.5)
    except EOFError:
        break except EOFError:
        break break k = raw_input() k raw_input() raw_input if len(k) > 0:
	    	a, b, x, y = map(float, k.strip().split(' '))
	    	print pow((a-x)*(a-x)+(b-y)*(b-y), 0.5)
     len(k) > 0 len(k) len k 0 a, b, x, y = map(float, k.strip().split(' ')) a map(float, k.strip().split(' ')) map float k.strip().split(' ') k.strip().split k.strip() k.strip k strip split ' ' b x y print pow((a-x)*(a-x)+(b-y)*(b-y), 0.5) pow (a-x)*(a-x)+(b-y)*(b-y) (a-x)*(a-x) a-x a x a-x a x (b-y)*(b-y) b-y b y b-y b y 0.5 k = raw_input() raw_input() k x, y = map(float, k.strip().split(' ')) map(float, k.strip().split(' ')) x a, b, x, y = map(float, k.strip().split(' ')) map(float, k.strip().split(' ')) a PI = 3.1415926535898 3.1415926535898 PI y = map(float, k.strip().split(' ')) map(float, k.strip().split(' ')) y b, x, y = map(float, k.strip().split(' ')) map(float, k.strip().split(' ')) b
from math import *
PI = 3.1415926535898
while True:
    try:
    	k = raw_input()
    	if len(k) > 0:
	    	a, b, x, y = map(float, k.strip().split(' '))
	    	print pow((a-x)*(a-x)+(b-y)*(b-y), 0.5)
    except EOFError:
        break